1. Field of the Invention
The invention relates to a device and a method for supplying a connecting element to a processing unit. A device of this generic type is disclosed, for example, by U.S. Pat. No. 4,348,796 A.
Connecting elements such as punch nuts, rivet nuts or press-in nuts are frequently connected to a work piece, for example to a metal sheet, in a processing machine, in particular in a press. In this case, during the joining operation in the press, the punch nut itself punches a hole in the metal sheet, while the rivet nut or the press-in nut is inserted into an opening already present in the metal sheet. The nuts are in each case first separated before being supplied to the press and, in accordance with the cycle rate of the latter, are supplied to a setting head incorporated in the press as a processing unit or fitted to the press. Presses of this type are used in particular in mass production, for example in the automobile industry, particular importance being attached to a fast process cycle and to interruption-free, reliable operation.
A device for transferring connecting elements to setting heads in a press is disclosed, for example, by Published, Non-Prosecuted German Patent Application DE 198 23 040 A1. In this case, the connecting elements are supplied by a sorting and conveying device, via a guide implemented as a guide hose, to a lower tool part of the press. From the latter, the connecting elements are transferred to the upper tool part via a transfer device and from there are distributed onward by a distribution station. The transfer of the connecting elements between the lower and upper tool part can be carried out only at the upper dead center of the press. The output of the press, that is to say the cycle rate that can be achieved, is severely restricted in this way.
European Patent EP 0 758 285 B1, corresponding to U.S. Pat. No. 5,887,339, discloses a device in which, in each case, a connecting element arrives in a loading position in a conveying section by being shot in via a hose. From the loading position, the connecting element is pushed further into the conveying section by a forward thrust element. A plurality of connecting elements is therefore lined up directly in a row in the conveying section being located as far as a setting head. The device is intended to permit a high number of strokes per unit time in a press, in that a sufficiently long period of time is available for reloading the connecting elements, for example nuts. For this purpose, the forward thrust element is normally in an ineffective position, what is known as a normal position, completely outside the conveying section. This results in that the forward thrust element is moved only to reload connecting elements into the conveying section and pushes the connecting elements lined up in a row in the direction of the press. In order to actuate the forward thrust element, the latter has a pneumatically actuated cylinder, whose piston acts via a pin in a slot in a forward thrust rocker, which can be pivoted into the conveying section through a slot. If the connecting element is unfavorably positioned in the conveying section, then there is the risk of blocking the forward thrust rocker during the attempt to pivot the latter into the conveying section. Furthermore, there is the disadvantage that, before a connecting element is shot in pneumatically, the forward thrust rocker has to be removed from the conveying section by actuating the pneumatic cylinder.
A supplying device for connecting elements, namely nuts, disclosed by U.S. Pat. No. 4,348,796, has a conveying section in which a spring-loaded pawl can engage, which is part of a forward thrust mechanism which operates with a hydraulic or pneumatic cylinder. During the reverse movement of the forward thrust mechanism, the pawl is displaced out of the conveying section by the nuts located in the conveying section and is drawn over the nuts. During the forward thrust of the nuts, on the other hand, the ratchet is always in its position engaging in the conveying section. The nuts are introduced into the supplying device, for example, in the form of continuous strips. Likewise, the nuts can be connected to one another by wires that can easily be divided.
A further supplying device for nuts is disclosed, for example, by U.S. Pat. No. 5,360,137. In this case, nuts which are supplied to a distributing device in a first direction are distributed into various channels in each case running at right angles to the supply direction by a number of forward thrust elements.